MODELING OF THE ACTIVE HARMONIC FILTER IN MAINS WITH LOAD WITH NONLINEAR CURRENT -VOLTAGE CHARACTERISTICS

Abstract

Modernized version of active power filter (APF) is proposed for electrical energy industry and electric drives application. Main functional area of APFs (APFs are transistor bridges, built up of different circuit design) is electrical energy industry. It pays attention for APF application as a part of variable frequency electric drive, which has «uncontrolled rectifier — DC link with capacitor and circuit with brake resistor — standalone voltage inverter» as a power circuit in this research paper. Appropriate applications of APF are highvoltage, high-powered variable frequency converters, such as drilling units, pumps and compressor for gas-compressor units. Another question at hand is making recommendations regarding improvement of two-level standalone voltage inverters as part of variable-frequency electric drives: substitution for multi-level inverters, on a first approximation — three-level inverters. This substitution allows reducing necessity of using expensive variable-frequency motors with advanced electrical isolation and non-conductive ceramic bearing parts. Multipurpose device, which contains multi-level variable frequency electric drive with multi-level voltage inverter and active power filter with proposed control algorithm is sophisticated electric drive control system. Such a design has a sparing effect for controlled object — induction motor; it doesn’t bring beneficial distortion in mains supply. Improved version of APF control system, were highspeed calculating unit is used, is tested by modeling with computer mathematic system MatLab. The calculating unit computes fundamental components of three phase currents. These components are used as a reference of APF control algorithm. Unlike popular designs of APF, which are adjusted to determined spectrum of harmonic distortion, proposed method makes wider application field of APF for usage with devices with different distortion types. Additionally, an advantage of proposed method is designing the APF for variablefrequency electric drives based on the required distortion power only. Comparison of phase currents and voltages quality with existing standards is done using shown variable-frequency electric drive of gas-compressor unit system as an example. In conclusion, modernized control algorithm of active power filter usage provides an opportunity to increase average power factor from 0.975 to 0.99, and improve greatly the quality and harmonicity of grid phase currents.